Prolonged constant load cycling exercise is associated with reduced gross efficiency and increased muscle oxygen uptake

This study investigated the effects of prolonged constant load cycling exercise on cycling efficiency and local muscle oxygen uptake responses. Fourteen well-trained cyclists each completed a 2-h steady-state cycling bout at 60% of their maximal minute power output to assess changes in gross cycling efficiency (GE) and muscle oxygen uptake (mVO2) at time points 5, 30, 60, 90, and 120 min. Near-infrared spatially resolved spectroscopy (NIRS) was used to continually monitor tissue oxygenation of the Vastus Lateralis muscle, with arterial occlusions (OCC) applied to assess mVO2 . The half-recovery time of oxygenated hemoglobin (HbO2 ) was also assessed pre and post the 2-h cycling exercise by measuring the hyperemic response following a 5-min OCC. GE significantly declined during the 2-h cycling bout (18.4 ± 1.6 to 17.4 ± 1.4%; P < 0.01). Conversely, mVO2 increased, being significantly higher after 90 and 120 min than at min 5 (+0.04 mlO2 /min/100 g; P = 0.03). The half-recovery time for HbO2 was increased comparing pre and post the 2-h cycling exercise (+7.1 ± 19s), albeit not significantly (d: 0.48; P = 0.27). This study demonstrates that GE decreases during prolonged constant load cycling exercise and provides evidence of an increased mVO2 , suggestive of progressive mitochondrial or contractile inefficiency

Protein Kinase A Governs Oxidative Phosphorylation Kinetics and Oxidant Emitting Potential at Complex I

he mitochondrial electron transport system (ETS) is responsible for setting and maintaining both the energy and redox charges throughout the cell. Reversible phosphorylation of mitochondrial proteins, particularly via the soluble adenylyl cyclase (sAC)/cyclic AMP (cAMP)/Protein kinase A (PKA) axis, has recently been revealed as a potential mechanism regulating the ETS. However, the governance of cAMP/PKA signaling and its implications on ETS function are incompletely understood. In contrast to prior reports using exogenous bicarbonate, we provide evidence that endogenous CO2 produced by increased tricarboxylic acid (TCA) cycle flux is insufficient to increase mitochondrial cAMP levels, and that exogenous addition of membrane permeant 8Br-cAMP does not enhance mitochondrial respiratory capacity. We also report important non-specific effects of commonly used inhibitors of sAC which preclude their use in studies of mitochondrial function. In isolated liver mitochondria, inhibition of PKA reduced complex I-, but not complex II-supported respiratory capacity. In permeabilized myofibers, inhibition of PKA lowered both the Km and Vmax for complex I-supported respiration as well as succinate-supported H2O2 emitting potential. In summary, the data provided here improve our understanding of how mitochondrial cAMP production is regulated, illustrate a need for better tools to examine the impact of sAC activity on mitochondrial biology, and suggest that cAMP/PKA signaling contributes to the governance of electron flow through complex I of the ETS

Effect of vitamin E (Tri E®) on antioxidant enzymes and DNA damage in rats following eight weeks exercise

<p>Abstract</p> <p>Background</p> <p>Exercise is beneficial to health, but during exercise the body generates reactive oxygen species (ROS) which are known to result in oxidative stress. The present study analysed the effects of vitamin E (Tri E^®) on antioxidant enzymes; superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (Cat) activity and DNA damage in rats undergoing eight weeks exercise.</p> <p>Methods</p> <p>Twenty four <it>Sprague-Dawley </it>rats (weighing 320-370 gm) were divided into four groups; a control group of sedentary rats which were given a normal diet, second group of sedentary rats with oral supplementation of 30 mg/kg/d of Tri E^®, third group comprised of exercised rats on a normal diet, and the fourth group of exercised rats with oral supplementation of 30 mg/kg/d of Tri E^®. The exercising rats were trained on a treadmill for 30 minutes per day for 8 weeks. Blood samples were taken before and after 8 weeks of the study to determine SOD, GPx, Cat activities and DNA damage.</p> <p>Results</p> <p>SOD activity decreased significantly in all the groups compared to baseline, however both exercised groups showed significant reduction in SOD activity as compared to the sedentary groups. Sedentary control groups showed significantly higher GPx and Cat activity compared to baseline and exercised groups. The supplemented groups, both exercised and non exercised groups, showed significant decrease in Cat activity as compared to their control groups with normal diet. DNA damage was significantly higher in exercising rats as compared to sedentary control. However in exercising groups, the DNA damage in supplemented group is significantly lower as compared to the non-supplemented group.</p> <p>Conclusions</p> <p>In conclusion, antioxidant enzymes activity were generally reduced in rats supplemented with Tri E^®probably due to its synergistic anti-oxidative defence, as evidenced by the decrease in DNA damage in Tri E^®supplemented exercise group.</p

The lipid droplet coat protein perilipin 5 also localizes to muscle mitochondria

Perilipin 5 (PLIN5/OXPAT) is a lipid droplet (LD) coat protein mainly present in tissues with a high fat-oxidative capacity, suggesting a role for PLIN5 in facilitating fatty acid oxidation. Here, we investigated the role of PLIN5 in fat oxidation in skeletal muscle. In human skeletal muscle, we observed that PLIN5 (but not PLIN2) protein content correlated tightly with OXPHOS content and in rat muscle PLIN5 content correlated with mitochondrial respiration rates on a lipid-derived substrate. This prompted us to examine PLIN5 protein expression in skeletal muscle mitochondria by means of immunogold electron microscopy and Western blots in isolated mitochondria. These data show that PLIN5, in contrast to PLIN2, not only localizes to LD but also to mitochondria, possibly facilitating fatty acid oxidation. Unilateral overexpression of PLIN5 in rat anterior tibialis muscle augmented myocellular fat storage without increasing mitochondrial density as indicated by the lack of change in protein content of five components of the OXPHOS system. Mitochondria isolated from PLIN5 overexpressing muscles did not possess increased fatty acid respiration. Interestingly though, 14C-palmitate oxidation assays in muscle homogenates from PLIN5 overexpressing muscles revealed a 44.8% (P = 0.05) increase in complete fatty acid oxidation. Thus, in mitochondrial isolations devoid of LD, PLIN5 does not augment fat oxidation, while in homogenates containing PLIN5-coated LD, fat oxidation is higher upon PLIN5 overexpression. The presence of PLIN5 in mitochondria helps to understand why PLIN5, in contrast to PLIN2, is of specific importance in fat oxidative tissues. Our data suggests involvement of PLIN5 in directing fatty acids from the LD to mitochondrial fatty acid oxidation

Methods for Assessing Mitochondrial Function in Diabetes

A growing body of research is investigating the potential contribution of mitochondrial function to the etiology of type 2 diabetes. Numerous in vitro, in situ, and in vivo methodologies are available to examine various aspects of mitochondrial function, each requiring an understanding of their principles, advantages, and limitations. This review provides investigators with a critical overview of the strengths, limitations and critical experimental parameters to consider when selecting and conducting studies on mitochondrial function. In vitro (isolated mitochondria) and in situ (permeabilized cells/tissue) approaches provide direct access to the mitochondria, allowing for study of mitochondrial bioenergetics and redox function under defined substrate conditions. Several experimental parameters must be tightly controlled, including assay media, temperature, oxygen concentration, and in the case of permeabilized skeletal muscle, the contractile state of the fibers. Recently developed technology now offers the opportunity to measure oxygen consumption in intact cultured cells. Magnetic resonance spectroscopy provides the most direct way of assessing mitochondrial function in vivo with interpretations based on specific modeling approaches. The continuing rapid evolution of these technologies offers new and exciting opportunities for deciphering the potential role of mitochondrial function in the etiology and treatment of diabetes

Mithochondrial function in human skeletal muscle : with special reference to exercise and training

The overall objective of this thesis was to study the adaptation of oxidative function in human skeletal muscle to acute exercise of different modes, intensities and durations, and to endurance training. The effects of endurance training on mitochondrial function were evaluated in cross-sectional and longitudinal studies by measurements of mitochondrial oxygen consumption in isolated mitochondria and permeabilised muscle fibres and measurements of mitochondrial ATP production rate in isolated mitochondria. A positive correlation was observed between maximal mitochondrial oxidative power measured in isolated mitochondria and permeabilised muscle fibres and other parameters related to local and whole body aerobic training status such as pulmonary maximal oxygen uptake, lactate threshold, and muscle activity of citrate synthase (CS). Previous studies have demonstrated that ADP and creatine are important regulators of oxidative phosphorylation. We found that the sensitivity of oxidative phosphorylation to ADP at the level of individual mitochondrion exhibits negative correlation with training status, whereas the creatine control of mitochondrial respiration is more pronounced in aerobically well-trained individuals. It is suggested that these adaptations may improve the potential for regulation of oxidative metabolism in trained muscle. The sensitivity of proton leakdependent oxygen consumption in isolated mitochondria to free fatty acids was up-regulated by a short-term endurance-training program. This may contribute to a higher basal metabolic rate in endurance-trained individuals. It is also suggested that this adaptation may prevent excessive free radical generation and enhance the potential for regulation of aerobic energy production in trained muscle. Exposure of isolated mitochondria to reactive oxygen species (ROS) reduced maximal ADP-stimulated respiration and P/O ratio and increased noncoupled respiration rate. The sensitivity of non-coupled respiration in isolated mitochondria to ROS was increased by 6 wk of endurance training, whereas the sensitivity of maximal ADP-stimulated respiration and P/O ratio to ROS was unaffected. These results indicate that inner mitochondrial membrane becomes more sensitive to oxidative stress after short-term endurance training. Activities of muscle antioxidative enzymes (SOD, GPX) and glutathione status were unaffected by training. This will result in a lowered antioxidative protection per mitochondrion, which may increase the susceptibility of inner membrane to oxidative stress. Maximal mitochondrial oxidative power in human vastus lateralis muscle was found to be intact or improved after high-intensity intermittent and moderate-intensity prolonged concentric cycling exercise as well as after eccentric cycling. Prolonged exercise increased the non-coupled mitochondrial respiration rate, which may contribute to the excess post-exercise oxygen consumption. After prolonged exercise an acute increase in muscle CS activity was observed. High-intensity intermittent exercise affected the ADP control of oxidative phosphorylation, as evidenced by transient decrease in ADP sensitivity of mitochondrial respiration in permeabilised muscle fibres. ADP sensitivity was unchanged after prolonged concentric and high-intensity eccentric exercise. Taken together these results indicate that mitochondrial function in human muscle is affected differently by exercise of different types. The effect of lactic acidosis on oxidative phosphorylation was evaluated in isolated mitochondria from rat skeletal muscle. It was demonstrated that acidosis induced on non-phosphorylating mitochondria reduces rate of subsequent maximal ADP-stimulated respiration. In contrast, when actively phosphorylating mitochondria were exposed to acidosis maximal ADP-stimulated respiration remained unchanged. On the basis of these results we suggested that the influence of lactic acidosis on muscle aerobic energy production may depend on the physiological conditions at the onset of acidity. Overall, the present investigations indicate that mitochondrial oxidative function is highly responsive to exercise. Endurance training induces adaptation of both quantitative and qualitative aspects of mitochondrial function, which improves the potential for metabolic control. The results suggest that acute physical exercise in humans is, in contrast to previous animal studies, well tolerated by skeletal muscle mitochondria